The formation of color photographic images by the image-wise coupling of oxidized primary aromatic amino developing agents with color forming or coupling compounds to form indoaniline, indophenol, and azomethine dyes is well known. In these processes, the subtractive process of color formation is ordinarily used and the image dyes customarily formed are cyan, magenta, and yellow, the colors that are complementary to the primary colors, red, green, and blue, respectively. Usually, phenol or naphthol couplers are used to form the cyan dye image; pyrazolone or cyanoacetyl derivative couplers are used to form the magenta dye image; and acylacetamide couplers are used to form the yellow dye image.
In these color photographic systems, the color-forming coupler may be either in the developer solution or incorporated in the light-sensitive photographic emulsion layer so that, during development, it is available in the emulsion layer to react with the color developing agent that is oxidized by silver image development. Diffusible couplers are used in color developer solutions. Nondiffusing couplers are incorporated in photographic emulsion layers. When the dye image formed is to be used in situ, couplers are selected which form nondiffusing dyes. For image transfer color processes, couplers are used which will produce diffusible dyes capable of being mordanted or fixed in the receiving sheet.
It is well known to incorporate sparingly-soluble alcohols in photographic color developing solutions which contain primary aromatic amino color developing agents. They are used to promote the reaction of the developing agent with the dye-forming couplers, i.e., to enhance coupling efficiency. Such alcohols are sometimes referred to as "development accelerators" or "development boosters". As indicated by the patent literature, for example, U.S. Pat. Nos. 2,304,925 and 3,814,606, benzyl alcohol is particularly effective for this purpose.
The use of sparingly soluble alcohols, such as benzyl alcohol, in photographic color developing solutions, to enhance coupling efficiency, has long presented a very difficult problem because of the poor solubility characteristics of these compounds. Thus, for example, dissolution of benzyl alcohol in the developing solution tends to be very slow and requires extensive stirring and/or heating. Moreover, the difficulties involved in dissolving benzyl alcohol can result in the formation of "tar" in the developing solution as a consequence of inadequate mixing and dissolution.
One approach to the problem of incorporating benzyl alcohol in photographic color developing solutions is to package the benzyl alcohol in the form of an aqueous liquid concentrate by utilizing a glycol, such as ethylene glycol, to solubilize the benzyl alcohol. This technique is disclosed in Surash, U.S. Pat. No. 3,574,619, issued Apr. 13, 1971. As described in this patent, to form the working strength developing solution the liquid concentrate containing the benzyl alcohol is admixed with one or more other liquid concentrates, containing the other ingredients of the developer formulation, and diluted with water. For convenience, all of the required liquid concentrates are typically packaged together in the form of a photographic processing kit. A second approach is to form an aqueous dispersion of the benzyl alcohol by use of an emulsifying agent such as hydroxyethyl cellulose. This technique is described in Kanous and Fassbender, U.S. Pat. No. 3,615,496, issued Oct. 26, 1971.
While the aforesaid prior art methods are effective for the purposes intended, they are costly and complicated because of the need to form liquid concentrates and do not always provide as easy a procedure for forming a tar-free working strength color developing solution as would be desirable. Thus, it is an objective of this invention to provide an improved and simplified technique whereby sparingly soluble alcohols, such as benzyl alcohol, can be incorporated in a photographic color developing solution in a simple and effective manner.